Patent GB-833036-A (GB)
Title: Method and apparatus for delivering combustible mixture to an internal combustion engine
IPC: F02M17/04
Filed: 1957-04-01
Abstract: 833,036. Charge forming devices. TILLOTSON MANUFACTURING CO. April 1, 1957 [June 4, 1996], No. 10525/57. Class 7(3) In a charge forming device including a body formed with a mixing passage and a fuel passage, a flexible diaphragm forms a wall of the fuel passage, a main orifice and a secondary orifice are formed in the wall of the mixing passage and are in communication with the fuel passage, there is provided a fuel inlet valve for the fuel passage, the inlet valve is coupled to the diaphragm for controlling the flow of fuel past the inlet valve, there is an element for delivering liquid fuel from the fuel passage through the main orifice into the mixing passage including a restricted region and the restricted region is of such a character and so arranged in relation to the fuel passage and the outlet of the main orifice whereby the resistance to fuel flow is effective so as to prevent movement of liquid fuel through the restricted region When fuel is discharging through the secondary orifice into the mixing passage. The charge forming device is particularly for two-stroke engines. The Specification refers to engines for powering lawn mowers, chain saws and small boats. The fuel inlet passage in the carburetter shown in Fig. 6 is arranged to be connected to a fuel pump situated remote from the carburetter or is adapted to receive fuel by gravity from a fuel pump. When this system of delivering fuel to the charge forming apparatus is utilized the diaphragm 32 is secured to the carburetter body by means of the plate 36. When a fuel feeding means is integrated or combined with the charge forming apparatus as shown in Fig. 9 a modified form of fuel inlet is employed. The fuel chamber or passage 30 is not vented to the atmosphere and fuel from the chamber or passage is delivered into the mixing passage of the carburetter by engine aspiration either through the main nozzle 48 or the idling and low speed orifices 50 and 52. As fuel is delivered into the mixing passage under the influence of reduced pressure transmitted through the fuel orifices to the fuel chamber 30 the flow of fuel into the mixing passage depletes the supply in the fuel passage or chamber 30. This causes the diaphragm to be flexed upwardly as viewed in Fig. 6 by atmospheric pressure causing the lever 74 to pivot counterclockwise. This moves the valve 90 away from its seat and facilitates the flow of fuel into the chamber 30. The flow of fuel into the chamber 30 and the lever is moved clockwise and the valve portion 90 again closes, until continued delivery of fuel into the mixing passage further reduces the pressure in the fuel passage or chamber 30. In actual practice it is found that a balance is maintained whereby the rate of fuel flow past the valve 90 is substantially equal to the rate of delivery of fuel from the chamber 30 into the mixing pasage the control valve being in slightly open position during most of the period of engine operation. The combined fuel feeding means and charge forming apparatus is shown in Fig. 9. The operation of the fuel feeding means is as follows: Assuming that the fuel flow control valve 90 is moved away from its seat to facilitate flow of liquid fuel into the cham-. ber 30 the varying pressures in the crank case of the engine with which the carburetter is used are transmitted through the ducts or passages 133, 132, 131 to vary the pressure in the pumping chamber 127. The varying pressures in chamber 127 cause reciprocating or pumping movements of the diaphragm 118 whereby fuel is supplied to the valve 90. The valve. means for controlling the flow of liquid fuel into and away from the fuel chamber 129 :are integral components of the diaphragm 118. As shown in Fig. 14, the inlet valve 136 and the outlet valve 138 are formed by punching or removing material of the diaphragm providing spaces 140, 141, the valve portions 136 and 138 being shaped as tongues which are adapted to be flexed. The diaphragm 118 may be of synthetic rubber or cloth such as nylon impregnated or coated with a material which is resistant to deterioration by hydrocarbon fuels. Three different forms of fuel conveying channel and fuel metering or regulating means for delivering fuel from the diaphragm chamber 30 to the main nozzle for normal operation and to the idling and low speed orifices for idling and low speed operation are described in the Specification. One of these is shown in Fig. 10. Passage 170 receives from chamber 30 through a passage 182. The needle valve 175 extends into a restricted passage 186 which conveys fuel from chamber 30 to the idling orifice 50 and the low speed orifice 52. The needle valve 179 co-operates with a restricted passage 188 for regulating or metering flow of fuel to the main nozzle or orifice 48 and into the mixing passage 12. It is found that the effectiveness of the liquid fuel seal against inward or reverse flow of air from the mixing passage through the main nozzle 48 between the points D to E (Fig. 9) involves or is dependent on the capillary meniscus or surface tension capping effect at the outlet of the main nozzle the frictional liquid resistance in the passage C, liquid resistance, a capillary seal set up or established at the annular zone B surrounding the metering valve for the main nozzle and the liquid resistance provided by the restricted passage A. It has been found that the factors such as the diameter length and contours of these liquid passages may be fashioned and the metering means adjusted or controlled to increase or decrease the combined or overall resistance to liquid flow and secure the sealing or check valve effect that is -necessary to the succesful operation of the carburetter. Specific dimensions of the parts are quoted in the Specification. The diaphragm 32 is made of very thin highly flexible cloth for example nylon fabric impregnated with a coating to render it impervious. Referring to Fig. 23, the diaphragm 32 is fitted into place with openings 46 received over pins 44 and the arrangement is such that the central zone of the diaphragm is forced or flexed inwardly in a loose wavy formation.